1. Field of the Invention
The invention relates to the field of medical mapping systems, namely systems and methods for guiding, steering and advancing an invasive medical device in a patient for the purpose of defining the physical boundaries and surface properties of a chamber or orifice.
2. Description of the Prior Art
All cardiac electrophysiologic procedures, as currently practiced, involve the use of intracardiac electrode catheters which are placed inside one or more of the four cardiac chambers. Occasionally one or more catheters is also placed in the pericardial space surrounding the heart. The catheters are used for recording intracardiac electrograms, and in many cases the catheters are also used for creating a 3-D representation of the relevant cardiac chamber. Mapping catheters contain an array of electrodes which are used for three purposes: (1) to record local and “far-field” intracardiac electrical activity, (2) to deliver ablative, or curative energy to endocardial surfaces, most commonly in the form of RF energy, and (3) for position location and creation of the chamber geometry. As the catheter is moved about the chamber, the geometric shell of the chamber is defined at the extreme limits of catheter travel, along with the electrical activity on that shell. When the physician determines that there is enough surface detail, the surface is considered to be fully mapped. The physician then uses the display of the endocardial electrogram on the geometric shell to determine specific locations to deliver therapeutic radiofrequency energy. Some electrophysiology laboratories deliver RF energy to specific sites, such as pulmonary vein ostia in the left atrium, without regard to the specific recorded electrogram at those sites. It is also common practiced to integrate or merge the 3-D geometry of the cardiac chamber with a pre-procedure representation of that chamber, usually obtained by a CT or MRI scan.
Prior to many ablation procedures, the relevant cardiac chamber is mapped in order to facilitate the movement of the catheter to precise anatomic regions which are responsible for initiating the arrhythmia. Once a circuit or an arrhythmogenic focus are found, or a specific aberrant tract is located, the catheter is directed the relevant endocardial surface site(s) and an electrode is placed in contact with the endocardial tissue. RF energy is then delivered from the electrode to the tissue to heat and ablate the tissue, thus eliminating the source of the arrhythmia.
Common problems encountered in this procedure are difficulty in precisely locating the aberrant tissue, and complications related to the ablation of the tissue. Locating the area of tissue causing the arrhythmia often involves several hours of electrically “mapping” the inner surface of the heart using a variety of mapping catheters, and once the aberrant tissue is located, it is often difficult to position or maintain the catheter at the desired position in the beating heart so that it continuously maintains contact with the desired tissue.
In the manual method of mapping coronary chambers, the physicians rely on their dexterity to manipulate mapping catheters about the chamber and into the associated vasculature. The density of the mapping data varies due to the time and attention the physician gives each part of the chamber, as well as to the anatomic variability found between individual patients i.e., in some patients certain cardiac anatomic regions are more difficult to reach than in other patients. In addition, the variable amount of force used by the physician in mapping will unevenly distend the chamber walls and create “false cardiac spaces,” as well as possibly distort the relationship between the pulmonary vein ostia and the associated left atrial body. The geometric definition of such ostia is critical in determining the locations for the delivery of therapeutic radiofrequency energy.
In both manual and automated mapping procedures, the catheter is swept about the inner surfaces of the cardiac chamber which is undergoing dynamic contractions under the systole/diastole cycle. The locally averaged (motion filtered) position of the catheter at its extreme limits is used to define the boundaries or endocardial surfaces of the relevant cardiac chambers. This type of catheter manipulation does not guarantee that the limit defined by the geometric map completely delineates the true anatomic borders of the cardiac chambers, but rather defines the limit of where the catheter has been.
Prior and related art associated with guiding and controlling an automated mapping and therapeutic procedure are extensive in scope, the discussion outlined by this application is centered on the ability of a novel magnetic chamber enabling such modality of guiding and controlling a mapping and other therapeutic tools in an automated fashion within the heart chambers of a patient.
The prior art as described by U.S. Pat. No. 3,708,772 (Le Franc) describes a highly compact magnetic lens arrangement which economically provides the highest field strength on the axis with the minimum beam half width and a minimum outer field strength of the coil winding which comprises two tubular shielding cylinder means of superconductive material coaxially aligned with the lens axis. The cylinder means each has a first end and a second end, said first ends being spaced from each other to define a unshielded lens gap between, said lens gap having a coil means positioned about the cylinder means to create a magnetic field, a cooling agent adapted to be present about the cylinder which cause a concentration of the magnetic field adjacent the particle beam, and a ferromagnetic ring-shaped pole shoe on each of said first ends of said cylinders for regulating and guiding the magnetic field.
Davis U.S. Pat. No. 4,057,748 teaches a travelling wave tube having a periodic permanent magnetic focusing structure provided with ferromagnetic plates having copper inserts which conduct heat away from the electron beam path and reduce the formation of hot spots.
Purnell U.S. Pat. No. 3,684,914 teaches a travelling wave tube including an envelope, an electron source for projecting an electron beam along a predetermined path in said envelope, a collector spaced from said source for intercepting and collecting electrons in the beam, a helical conductor disposed within said envelope along the path of said beam for supporting and projecting an electromagnetic wave in coupled relationship to the beam for interaction therewith, a periodic permanent magnet focusing assembly having a succession of alternate high thermal conductivity conducting bars and magnetic plates having aligned apertures to define an envelope portion which accommodates the helix support assembly and helix and a plurality of magnet bars disposed between plates to form a succession of longitudinal magnetic fields in coupled relationship with the beam to focus the same as it travels along the envelope portion.
Carson, et al. U.S. Pat. No. 6,078,872 titled “Magnetic lens, method and focus volume imaging MRI” teaches methods for suppressing noise in measurements by correlating functions based on at least two different measurements of a system at two different times. In one embodiment, a measurement operation is performed on at least a portion of a system that has a memory. A property of the system is measured during a first measurement period to produce a first response indicative of a first state of the system. Then the property of the system is measured during a second measurement period to produce a second response indicative of a second state of the system. The second measurement is performed after evolution duration subsequent to the first measurement period when the system still retains a degree of memory of an aspect of the first state. Next, a first function of the first response is combined with a second function of the second response to form a second-order correlation function. Information of the system is then extracted from the second-order correlation function.
In general, the prior art is centered on the ability of microscopic resonance imaging, spectrometry, and general resonance imaging to form a coherent magnetic field for use in MR imaging. Maxwell's equations place restrictions on the properties of magnetostatic fields in free space. It is impossible for the magnitudes of the components of the magnetic field vector BX, BY, or BZ to have a local minimum or maximum in free space. Additionally, the magnetic field magnitude, |B|, cannot have a local maximum, but it can have local minimum in free space. Localized minimums have been generated with current carrying structures and used in the fields of plasma confinement, neutral particle trapping, and levitation. Others have also proposed magnetic resonance imaging techniques that were based on different physical principles for creating what the papers termed as an imaging focus point, and relied on the magnetic field gradients produced by the three-dimensional current carrying wires. See, Damadian, et al., “Field Focusing Nuclear Magnetic Resonance (FONAR): Visualization of a Tumor in a Live Animal,” Science 194, 1430 (1976); Hinshaw, “Image Formation by Nuclear Magnetic Resonance: The Sensitive Point Method,” J. Appl. Phys. 47, 3709 (1976). The current carrying structures limit practical extensions of the technique. All the above noted patents and journal publications are the results of the ability of microscopic resonance imaging, spectrometry, and general resonance imaging to form a coherent magnetic field for use in MR imaging. The novel and application of the waveguide and its magnetic aperture depart from the prior art due to the embodiments which this application teaches.
What is needed is a new waveguide and magnetic aperture that enables the creation of an electroanatomic map by using an apparatus that automatically performs the task of mapping of an anatomical site.